Thermic flash-over current- and phaseinterrupting protective relay



3,475,709 INTERRUPTING L 1969 T. s. BASSE THERMIC FLASH-OVER CURRENT-AND PHASE PROTECTIVE RELAY Filed June 16, 1967 FIG-.5

INVENTOR. TAGE sTENBERG BASSE ATTORNEY United States Patent THERMICFLASH-OVER CURRENT- AND PHASE- INTERRUPTING PROTECTIVE RELAY- TageStenberg Basse, Nordborg, Denmark, assignor to Danfoss ved ing. M.Glausen, Nordborg, Denmark, a corporation of Denmark Filed June 1 6,1967, Ser. No. 646,705 Int. Cl. H01h 61/01, 71/16 US. Cl. 337-44 ClaimsABSTRACT OF THE DISCLOSURE A thermally actuated protective relay for amultiphase circuit comprises a plurality of approximately parallelbimetallic strips, a pair of slide rods actuated by the concerted actionof the strips, a lever-swingable by the slide rods and a switch actuatedby the lever. The point at which the lever is connected to the switch isselected so that it does not move materially when all of the strips andslide rods move together. However, when movement of one slide rod isselectively limited, the resulting relative movement of the slide rodsproduces angular movement of the lever to actuate the switch. The switchis also actuated in the event the current in one phase isinterrupted oris excessive. Preferably the switch is a snap switch having a firstpivoted arm connected to the aforementioned lever, a second pivoted armcarrying a movable contact and a spring connecting the two arms-Movement of the movable contact is preferably limited by a back contactwhich can 'be selectively positioned to provide either one or two stablestates for the movable contact as desired.

The present invention relates to protective relays and particularly to arelay for protecting a multiphase circuit both against overload andagainst current interruption or abnormal current in one phase.

In accordance with the invention, a single set of contacts is utilizedto provide protection both against excess current and against failure inone phase. However, despite use of the same set of contacts, the twomodes of protection are independent of one another.

The relay in accordance with the invention preferably comprises asnap-acting switch which is actuated by a relatively small movement ofthe actuating member. Moreover, the switch provides two modes ofoperation in one of which the relay automatically resets itself as soonas abnormal conditions in the circuit have ceased and in the other whichthe relay, when tripped must be manually reset. A member which isselectively positioned to select the mode of operation is also operableto reset the relay manually when it is operating in the non-automaticmode. A further feature of the invention is that the relay cannot bemanually reset so long as the abnormal conditions which produced thetripping of the relay still persists.

The nature and advantages of the protective relay in accordance with theinvention will be more fully understood from the following descriptionof preferred embodiments shown by way of example in the accompanyingdrawings in which:

FIG. 1 is a schematic illustration of a relay in accordance with theinvention for a 3-phase circuit, the relay being shown in coldcondition,

FIG. 2 shows the relay during normal operation,

FIQ. 3 shows the relay being tripped 'by reason of excessive current,

FIG. 4 shows the relay being tripped by interruption of current in onephase and FIG. 5 is a schematic illustration of a snap switcharrangement incorporated in a relay of the kind shown in FIGS. 1 to 4.

The relay shown by Way of example in FIGS. 1 to 4 is for the protectionof a 3-phase alternating current circuit, e.g., the three wire supply ofa 3-phase motor. For this purpose, the relay comprises three bimetallicstrips 1, 2 and 3 which are heated respectively by the current of thethree phases. The respective thermal windings are not shown in thedrawings but are connected in usual manner so that each of thebimetallic strips is heated in proportion to the current flowing in therespective line of the 3-phase circuit. The three bimetallic strips 1, 2and 3 are suitably anchored on a suitable support as indicated at 1a, 2aand 3a. Free end portions of the bimetallic strips are movable laterallyin proportion to the temperature to which the strips are heated by therespective thermal windings. As illustrated in the drawings, the freeupper end portions of the strips move toward the left as the strips areheated.

The three bimetallic strips cooperate with two slide rods 4 and 5 whichextend transversely of the strips and are longitudinally slidable insuitable supports 6 and 7. The two slide rods 4 and 5 are approximatelyparallel to one another and are spaced apart, the upper slide rod 5being located near the upper ends of the bimetallic strips 1, 2 and 3while the lower slide rod 4 is located at a position spaced from theupper ends of the strips by distance amounting, e.g., to about /3 to /6the length of the strips. The lowest slide rod 4 is provided withshoulders 4a, 4b and 46 which are engageable respectively by thebimetallic strips 1, 2 and 3 when the strips move in the directiontoward which they are flexed when heated. The upper slide rod 5 isprovided with shoulders 5a, 5b and 5c which are engageable respectivelywith the opposite sides of the bimetallic strips.

The slide rods 4 and 5 are pivotally connected by links 8 and 9 with alever 10 which extends downwardly toward the anchored ends of thebimetallic strips and is connected by a link 11 with the movable contactelement 12a of a switch 12 having a stationary contact 12b. Anadjustable stop shown in the form of a screw 13 is provided forselectively limiting the movement of one of the slide rods 5.

The point of connection 11 of the actuating lever 10 with the movableelement 12a of the switch 12 is selected in relation to the length ofthe bimetallic strips and the distance between the slide rods 4 and 5 sothat the connection 11 remains substantially stationary when the threebimetallic strips 1, 2 and 3 bend together by approximately the sameamount and the shoulders 4a, 4b and 4c of slide rod A and shoulders 5a,5b and 5c of slide rod 5 remain in contact with the respective strips.This is seen by comparison of FIG. 1 which shows the relay in coldcondition with FIG. 2 where the relay is shown in normal operatingcondition with all of the strips having flexed toward the left. It willbe seen that the point of connection 11 of the actuating lever 10 withthe switch 12 has remained in essentially the same position. It has beenfound that the desired relationship is obtained by the formula where xis the length of the lever 10 a is the distance between the slide rods 4and 5 L is the length of the bimetallic strips The positon of the screw13 is adjusted so as approximately to engage the upper slide rod 5 whenthe bimetallic strips 1, 2 and 3 are heated by normal current 3 Iflowing in the 3-phase circuit. This condition is illustrated in FIG. 2.If the current is increased above its normal value, the resultingadditional heating effect tends to flex the strips 1, 2 and 3 farthertoward the left. However, since the upper slide rod is held stationaryby engagement with the screw 13, only the lower slide rod 4 can move.The resulting relative movement between the slide rods produces angularmovement of the lever about the link 8 as a fulcrum so as to open theswitch 12 as illustrated in FIG. 3. It will be understood that byadjustment of the screw 13, it is possible to select the point at whichthe relay will trip. Once the slide rod 5 has engaged the screw 13,tripping of the relay is effected by only a short additional movement ofthe slide rod 4 by the bimetallic strips.

FIG. 4 illustrates the condition which arises in the event the currentin one phase is interrupted or materially decreased. By way of example,it is assumed that there is no current in phase 2 while the current inphases 1 and 3 is normal. Since the bimetallic strip 2 is not heated andhence not flexed, engagement of strip 2 with the shoulder 5d of sliderod 5 holds the silde rod against movement toward the left. However,slide rod 4 is moved toward the left by the flexing of bimetallic strips1 and 3 by normal heating current. The resulting relatively movement ofthe slide rods 4 and 5 produces angular movement of the actuating lever10 so as to open the switch 12 as is illustrated in FIG. 4. In thismanner, tripping of the relay is effected by any material unbalancebetween the three phases. The relay is sensitive in that opening of theswitch 12 is effected by relatively slight relative movement of theslide rods 4 and 5. Moreover, tripping of the relay by reason ofunbalance of the phases is completely independent of the adjustment ofthe relay for overload current by means of the screw 13.

In FIG. 5, the switch is shown as a snap switch which is operated by theactuating lever 10. The switch comprises a first lever arm 14 pivotallymounted at 15 and a second lever arm 17 pivotally mounted at 18. The twolever arms 14 and 17 are connected by a tension spring 19. The actuatinglever 10 of the relay is connected to the first operating arm 14 of thesnap switch through a pivotal connection 11. The second operating arm 17of the snap switch carries a contact which is engageable with a fixedcontact 21 when the switch is in closed position as illustrated in FIG.5. When the first lever arm 14 is moved to the left by the actu'atinglever 10 so that the lower end of the arm to which spring 19 is attachedmoves to the left of the pivot 18, the spring 19 causes the second leverarm 17 to move to the left with a snap action. Movement of the secondlever arm toward the left is limited by a back contact 22 carried by aleaf spring 23.

Means is provided for selectively positioning the back contact 22 in afirst position as shown in solid lines in FIG. 5 and a second position22' as indicated in dotted lines. When the back contact 22 is in theposition shown in solid lines, the lever arm 17 carrying contact 20 hastwostable positions with the contact 20 engaging contact 21 and 22respectively. When the back contact 22 is in the dotted line position22', the lever arm 17 has only one stable position with the contact 20engaging contact 21 and will return to that position as soon as theactuating force exerted by lever 10- is removed. Hence in the lattercase, the relay automatically resets itself upon termination of thedisturbance which caused tripping of the relay while in the former case,the switch remains in tripped condition and must be reset, e.g.,manual-1y.

The means for selectively positioning the back contact 22 is shown byway of example in FIG. 5 as a slide bar 24 having an inclined endengageable with an inclined end portion of the spring 23 which carriesthe back contact 22. A spring tends to hold the slide bar 24 inretracted position as shown in the drawing. When the slide bar 24 ispushed inwardly against the force of spring 25, the inclined inner end24a of the bar 24 engages the inclined end portion on leaf spring 23 tomove the spring and the back contact 22 to the dotted line position 22'.The slide bar 24 can, if desired, be latched in its inner position by asliding bolt 26 engageable with a aperture 24b in the slide bar.

If the relay is tripped when the slide bar 24 is in the retractedposition shown in solid lines in FIG. 5, the force exerted on lever arm14 by the actuating lever 10 causes the lever arm 14 and also the leverarm 17 to swing to the left to break the contact between contacts 20 and21 and to bring the movable contact 20 into engagement with the backcontact 22. Only slight movement of the lever 10 is required to trip therelay. If the disturbing force which caused tripping of the relay is nowremoved, contact 20 remains in engagement with contact 22 so that therelay is not self resetting. Resetting of the relay can be effected bymoving the slide bar 24 inwardly and thereby moving the back contact 22to the dotted line position 22' whereupon the spring 19 will elfectfurther movement of the lever arm 17 to bring contact 20 into engagementwith fixed contact 21. If, however, the disturbance which causedtripping of the relay has not been removed, a force will still beexerted on lever arm 14 by the actuating lever 10 and hence the contact20 will remain in engagement with back contact 22 even when in thedotted line position 22'. Hence the relay cannot be manually reset solong as a disturbance continues.

If the relay is tripped when the slide "bar 24 is held in its innerposition by the bolt 26, the force exerted on the lever arm 14 by theactuating lever 10 will cause the lever arm 17 to swing to the leftuntil contact 20 engages the back contacting position 22' As soon asdisturbance which caused tripping of the relay is removed, the lever arm17 will return to the position shown in FIG. 5 with contact 20 inengagement with contact 21. The relay in this condition is thusautomatically resetting.

It will thus be seen that the member 24 serves not only to select themode of operation of the relay so as to automatically resetting ornon-automatic as is desired but serves also to reset the relay when inits non-automatic mode of operation.

While preferred embodiments of the invention have been illustrated byway of example in the drawings, it will be understood that manyalterations can be carried out without deviating from the fundamentalconcept of the invention. For example, the adjustment member illustratedschematically as the screw 13 may be a sliding rod positioned by abimetallic strip exposed to ambient tem perature so as to compensate forthe effect of variation of room temperature on the operation of theactuating bimetallic strips 1, 2 and 3. When the slide rods 4 and 5 areconnected by means of a spring, the pivotal connections 8 and 9 betweenthe slide rods and the actuating lever 10 can be formed as recesses ornotches in the slide rods engaging suitable fulcrum edges on theactuating lever. Still other variations and modifications will beapparent to those skilled in the art.

What I claim is:

1. A thermal protective relay for a multiphase circuit comprising aplurality of approximately parallel bimetallic strips each heated bycurrent of one phase of said circuit, each of said strips being anchoredat one portion and having a portion that is movable upon heating of thestrip, two approximately parallel slide rods. spaced from one anotherand mounted for longitudinal movement transversely of said movableportions of said strips, one of said slide rods being disposed closelyspaced to a point of anchorage of each rod and the other rod beingdisposed spaced from each point of anchorage about /6 to about /3 theaxial length of said strips, one of said slide rods having abutmentsengageable with one side of each of said strips respectively and theother of said slide rods having abutments engageable with the oppositeside of each of said strips respectively, whereby said slide rods aremovable longitudinally by said strips, a lever extending transversely ofsaid slide rods and flexibly connected thereto, a switch actuatable bysaid lever, said lever having a portion extending approximately parallelto said strips and in a direction generally toward the anchored portionsof said strips, means connecting said extending portion of said leverwith said switch, said connecting means being located at a point on saidlever which remains approximately stationary when said strips and sliderods move together, and means selectively limiting movement of one ofsaid slide rods to cause relative movement of said slide rods when saidlimit is reached and thereby produce angular movement of said lever toactuate said switch.

2. A relay according to claim 1, in which said switch is a snap-actingcomprising a first pivoted arm connected with said lever, a secondpivoted arm approximately in line with said first arm and carrying amovable contact and a tension spring connecting said arms.

3. A relay according to claim 2, in which said switch further comprisesa fixed contact, and a back contact engageable by said movable contactand means for selectively positioning said back contact in a firstposition providing two stable positions for said movable contact inengagement with said fixed contact and back contact respectively and asecured position providing only one stable position for said movablecontact in engagement with said fixed contact. I

4. A relay according to claim 3, in which said means for selectivelypositioning said back contact comprises means for manually resettingsaid relay.

5. A thermal protective relay for a multiphase circuit comprising aplurality of approximately parallel bimetallic strips each heated bycurrent of one phase of said circuit, each of said strips being anchoredat one portion and having a portion that is movable upon heating of thestrip, two approximately parallel slide rods spaced from one another andmounted for longitudinal movement transversely of said movable portionsof said strips, one

of said slide rods having abutments engageable with one side of each ofsaid strips respectively and the other of said slide rods havingabutments engageable with the opposite side of each of said stripsrespectively, whereby said slide rods are movable longitudinally by saidstrips, a lever extending transversely of said slide rods and flexiblyconnected thereto, a switch actuatable by said lever, said lever havinga portion extending approximately parallel to said strips and in adirection generally toward the anchored portions of said strips, meansconnecting said extending portion of said lever with said switch, saidconnecting means being located at a point on said lever which remainsapproximately stationary when said strips and slide rods move together,means selectively limiting movement of one of said slide rods to causerelative movement of said slide rods when said limit is reached andthereby produce angular movement of said lever to actuate said switchand said slide rods being spaced from each other axially along thestrips and said lever has a determined length by the formula:

a 2.La

where x is the length of the lever a is the distance between the sliderods, and L is the length of the bimetallic strips References CitedUNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner R. L. COHRS,Assistant Examiner US. Cl. X.R. 20067; 33749

